This simply isn't true. Longer and more accessible beta testing means more chances of players finding obscure bugs that the developers would never had a chance to flush out. Having 2 million people participate in a beta that lasts 8 months is bad, but so is having less than 100k participating in a beta that lasts 2-3 months.
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You know what would be swell? If Blizzard would buck up and release quality content that was adequately user tested and nigh bug free at a pace that was just slightly faster than their current snail race pace. But asking for that is like asking for black voodoo magic, someone is going to end up on a stake and crispy.